Electrostatic painting of various vehicle components presents an attractive and cost effective scheme as compared to usage of a conventional paint line. Electrostatic painting of vehicle parts, such as doors, hoods, quarter panels, and other vehicle skin parts can be routinely performed. Owing to the high visibility and environmental exposure encountered by such vehicle parts, a high quality paint finish surface is demanded that is commonly referred to in the industry as a Class A finish associated with a high degree of reflectivity and a surface free of visual defects. Electrostatic painting requires the part to be electrically conductive and support an electrical potential on the part needed to attract oppositely charged paint aerosol droplets to the part. Early attempts at producing inexpensive molding compound components amenable to electrostatic painting involved the application of an electrically conductive primer. With the primer application adding considerable cost and the primer application defects being manifest in the resulting painted article. As a result, these previous attempts to make sheet molding compound conductive articles were relegated to vehicle portions other than the vehicle skin, such as radiator brackets and wheel wells.
The development of an inherently conductive sheet molding compound obviates the need for the application of a conductive primer coat. Such a conductive sheet molding compound (SMC) is detailed in U.S. Pat. No. 6,001,919. As tolerances for the acceptable amount of SMC article shrinkage relative to mold specifications decreases, as well as increased demands as painted surface finish attributes, low profile additives are increasingly found in SMC. Representative of these high-performance SMC formulations inclusive of low profile additives are those current marketed by Continental Structural Plastics under the trade name TCA. The inclusion of low profile additives is compatible with a conductive particulate to render an SMC article amenable to electrostatic painting, however, the inclusion of loadings of conductive particulate necessary to make an article sufficiently conductive, modifies the flow properties of the molding compound resins, leading to inhomogeneous molded articles, degrades the surface finish, and the higher viscosity forces molding filling conditions that degrade the conductivity of a given volume of conductive filler.
Thus, there exists a need for a molding compound composition that is conductive to provide a high quality paint finish provided through electrostatic painting that has handling properties allowing mold filling without damaging the delicate structure of high surface area conductive particles.